Galvanic cells, such as alkaline cells, are generally designed to vent when the internal pressure exceeds a predetermined amount. When exposed to an abuse condition, such as being charged to an excessive degree, the cell will normally vent and allow the electrolyte to escape. Although it is preferable to have the electrolyte escape rather than have the cell rupture from internal pressure buildup, electrolyte leakage can be potentially dangerous to persons and destructive to equipment.
Cell manufacturers have used a number of approaches to resolve the problem of electrolyte leakage. One of the most common methods of preventing seal rupture due to abuse charging or the like is to insert a diode in the battery's electrical circuit. By eliminating the possibility of charging the cells, internal gas is not generated and the seal never ruptures. Another electrically related mechanism is a belleville shaped "flip switch". This device is triggered by bulging of the cell bottom which causes a washer to invert and thereby break electrical contact. Another method involves the use of absorbents or electrolyte thickeners. The absorbent materials are usually located outside the seal area and beneath the cell's cover or jacket. As electrolyte escapes from a ruptured seal, the liquid is absorbed. Spew thickeners are mixed with the electrolyte and therefore are contained within the cell. The objective of the thickener is to slow down and/or absorb any leakage that may occur. The disadvantage of using either an absorbent or a thickener is that both materials tie up space that otherwise could be used for active materials of the cell. A third procedure is to use an outer container and end covers as an electrolyte containment system to provide space to contain the electrolyte that escapes.
U.S. Pat. No. 3,676,221 discloses a battery comprising a plurality of stacked, disk-like sealed cells secured together by cups fitted over one cell of each pair and having bottoms spot-welded to the next cell and sidewalls spot-welded to the interfitting cell. A heat-shrunk sheath encloses the battery and has caps forming the poles. Between each pair of cells is a circular disc of insulating material against which the cup bottoms bulge upon expansion of the contents of the cells, thereby breaking the welds and electrically disconnecting the cells.
U.S. Pat. No. 4,025,696 describes a disk shaped washer which inverts after the bottom bulge exceeds a predetermined value. Prior to activation, the washer's inside diameter is slanted toward the container. As the container bulges, the bottom of the container pushes against the washer and eventually causes the washer to invert. This inversion electrically separates the bottom cover from the container. An open circuit is the net result.
U.S. Pat. No. 3,775,661 describes a cell in which internal pressure forces a diaphragm against a switch which electrically disconnects a charging device. The diaphragm is located inside a venting device which is attached to one end of the cell.
U.S. Pat. No. 2,651,669 describes a bulge activated switch that can be incorporated into a single cell battery or a multiple cell battery and operable such that the bulge can be used to open a switch or switches that control the cell's discharging and/or charging circuits.
U.S. Pat. No. 3,617,386 describes a cell in which a thin sheet of metal with "spring back" ability is positioned between the seal and cover of the cell so as to break the cell's electrical circuit when the bulge becomes excessive.
It is therefor an object of this invention to provide a galvanic cell with means for electronically isolating one terminal of the cell from the cell's electrochemical system upon a predetermined bulge in the cell's housing.
Another object of this invention is to provide means for electrically isolating one terminal of a galvanic cell from the cell's electrochemical system upon a predetermined bulge in the cell's housing that will occupy a minimum space requirement so as not to diminish the space allocated for the active components of the cell.
Another object of this invention is to provide a sealed galvanic cell with means for electrically isolating one terminal of the cell from the electrochemical system of the cell upon a predetermined bulge in the cell's housing that is easy to make, cost effective and easy to assemble.
The foregoing and additional objects will become more fully apparent from the following description and the accompanying drawing.